Amazon has Sunny Days Entertainment Expandable Ball for $6. Shipping is free w/ Prime or on orders of $35+.

Features:

• With the Expandable Ball, it's hours of fun to pull, push, roll and toss! Measuring 13 inches in diameter when fully opened, there's so much sensory fun to be had
• Made of durable, non-toxic material for long lasting use, and its shape allows it to withstand tough play
• Ages 3 and up.